1. Field of the Invention
The present invention relates to centrifugal submersible pumps. More particularly, the present invention relates to such a pump useful in removal of methane from a water-methane solution in a downhole well located in coal deposits.
2. Description of the Related Art
There are several problems connected with the downhole pumping of water containing dissolved methane gas from a source such as a coal field. These problems generally result in premature failure of the submerged pump. One problem is vapor lock which occurs when the flow of water is too low compared with the amount of gas present. Another is the presence of large coal particles which flow through the pump and cause damage thereto. Yet another is excessive wear in a water-coal slurry environment.
U.S. Pat. No. 4,708,589, issued Nov. 24, 1987, to Nielson et al., describes a submersible pump of the general type as the present invention. This design may be adequate for petroleum wells, but would suffer from unacceptable wear in a water pumping environment where entrained methane and coal particles are present.
U.S. Pat. No. 4,741,668, issued May 3, 1988, to Bearden, describes a submersible pump having centrifugal pump stages with abrasion resistant impeller hub. This design has the shortcoming of having rubbing parts, reducing the life of the pump, particularly in the environment of a water well having coal particles having coal particles therein.
U.S. Pat. No. 3,975,117, issued Aug. 17, 1976, to Carter describes a submersible pump having an inducer and a multistage centrifugal pump section at opposite ends of the driving motor in a pump for cryogenic or boiling fluids, particularly in a tanker ship or storage tank. This design is not appropriate where relatively large solid particles such as coal may be present in the fluid being pumped.
U.S. Pat. No. 3,975,113, issued Aug. 17, 1976, to Ogles describes a submersible pump useful for downhole pumping of water. This design is not adapted to pumping water containing high levels of methane or other gas and would be subject to damage by large particles and loss of prime by large slugs of gas.
U.S. Pat. No. 3,961,758, issued Jun. 8, 1976, to Morgan describes a submersible pump useful for pumping liquids and liquid slurries such as in a sewage collection tank, and provides a grinder at the inlet. This design would not be useful in a downhole water-methane solution environment as it is subject to vapor lock from gas slugs and subsequent loss of prime.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a centrifugal submersible pump solving the aforementioned problems is desired.
The present invention is a submersible pump specifically designed for downhole pumping of methane-saturated water from wells drilled in coal formations. The centrifugal pump configuration has an electric motor driving a vertical shaft having centrifugal impellers distributed therealong, each impeller being located in a diffuser, stationary with regard to the pump wall to form a multi-stage pump useful in the petroleum industry, but is modified in several respects for adaptation to the specified use. Most notably, a shroud, concentric with the pump wall and forming an annulus which is sealed relative to the lower portion of the pump wall is provided such that all fluid must enter holes near the top of the shroud and travel downward through the annulus to a point below the pump inlet. A charge impeller is located near the pump inlet and above the driving motor, followed by a solids grinder to grind larger coal particles carried within the pumped fluid before entering the first centrifugal stage of the pump. The charge impeller and solids grinder are mounted on the same rotating shaft as the centrifugal impellers and turn at the same rate. The multi-stage centrifugal pump may be provided with stages of diminishing volume as the methane gas and liquid mixture becomes more and more compressed as it travels upward through the pump. Another charge impeller may be located at the upper end of the shaft at the pump outlet to boost flow upward into a vertical pipe sealed to the pump for carrying the compressed fluid to the surface for separation. Pressure equalization vents are located to allow flow of fluid from the third centrifugal stage to the annulus between the shroud and the pump wall to maintain pump prime when encountering a slug of gas in the intake. Pump stage centrifugal impellers each have a hub extending upward and downward along the length of the driving shaft such as to rest upon each other in turn, while avoiding contact with the stationary diffusers.
Accordingly, it is a principal object of the invention to provide a centrifugal submersible pump particularly adapted for pumping methane-saturated water from a well in a coal bed to the surface for separation and recovery of methane gas.
It is another object of the invention to provide a centrifugal submersible pump as above having a concentric shroud located along its lower portion and forming and annulus therewith and sealed to the pump housing both below the pump inlet and the shroud upper end wherein holes are provided near the upper end for fluid flow into the annulus and downward into the pump inlet.
It is a further object of the invention to provide a centrifugal submersible pump as above having a centrally rotating shaft extending upward from a motor and having a flow inducer located thereon in the vicinity of pump inlet openings.
Still another object of the invention is to provide a centrifugal submersible pump as above having a solids grinder located along the shaft above the flow inducer to reduce the size of any coal particles entering the pump.
Yet another object of the invention is to provide a centrifugal submersible pump as above having multiple stages reducing in volume as the pumped methane-water mixture becomes compressed due to increasing pressure as it travels upward through the pump.
Still another object of the invention is to provide a centrifugal submersible pump as above having a centrifugal impeller within each stage and wherein each impeller is keyed for rotation to the rotating shaft by a hub extending upward and downward along the shaft so as to respectively rest upon each other so as to avoid an contact with surrounding diffusers, minimizing wear of pump parts.
Yet another object of the invention is to provide a centrifugal submersible pump as above having pressure equalizer conduits communicating between the third pump stage from the bottom and the shroud-enclosed annulus to maintain pump prime when encountering slugs of gas at its intake.
It is an object of the invention to provide improved elements and arrangements thereof for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.